1. Field of the Invention
The invention relates to a molding method for various conductive plates such as the separator for a fuel cell and a molding apparatus for the same.
2. Description of the Related Art
One type of the separators for the fuel cell, as an example of the separator, includes a plurality of carbon rods implanted in the substrate made of synthetic resin as protruded portions, as disclosed in Japanese Patent Application Laid-Open No. 5-74469. In order to form that separator, a substrate made of synthetic resin and a plurality of carbon rods formed of carbon powder or the like are prepared and then, these carbon rods are installed in mounting holes made in the substrate. That is, the separator is formed by assembling the carbon rods and the substrate integrally with each other.
The invention relates to a molding method for molding the conductive plate having a plurality of protruded portions which are protruded in a single side or both sides of the substrate and a molding apparatus.
In the molding method for the conductive plate according to a first aspect of the invention, the substrate having the through holes at positions corresponding to the protruded portions is employed and the same substrate is sandwiched between both dies. Then, raw powder is filled into the respective housing portions provided opposing the respective through holes in the substrate through the through holes in order to form the protruded portions and then, by heating the raw powder under pressure, the protruded portions are formed integrally with the substrate.
In the molding method according to the first aspect of the invention, the respective protruded portions can be formed integrally with the substrate by heating the raw powder filled in each housing portion in each of both dies under pressure. Therefore, when forming the conductive plate of this type, it is not necessary to prepare the protruded portions independently, thereby making it possible to abolish the work for forming the protruded portions separately. Further, the work for fitting the separately formed respective protruded portions into the through holes can be abolished. Consequently, this type of the conductive plate can be formed efficiently in a short time and at a low cost.
A substrate made of synthetic resin may be employed as the substrate and the raw powder in which carbon powder is mixed with binder resin may also be employed. Further, thermosetting resin may be employed as the binder resin. Consequently, this type of the conductive plate, particularly, a preferable separator for the fuel cell can be produced.
The molding method according to the first aspect of the invention may be constructed such that by supplying a power to the raw powder filled in each housing portion in both dies, the raw powder is heated with heat generated by resistance. In this case, it is desirable to supply power to the raw powder filled in each housing portion in both dies.
With this structure, time required for heating the raw powder filled in each housing portion can be reduced largely, thereby leading to a large reduction of total processing time for the conductive plate. Further if the raw powder filled in the respective housing portions is supplied with power in series connection, current is applied to the raw powder in each housing portion equally and rapidly. Consequently, the respective portions of the raw powder can be heated efficiently with heat generated by resistance.
Further, in the first aspect of the invention, it is permissible to employ a mold having an opening with a diameter slightly larger than the through hole of each housing portion in the substrate to be filled with the raw powder.
In this case, when the raw powder filled in each housing portion is heated under pressure, part of the raw powder flows out around the periphery of the opening of each through hole in the substrate and hardens. As a result, joint area of the protruded portion to the substrate is increased so that the joint strength at each protruded portion is improved and at the same time, air-tightness between each protruded portion and each through hole in the substrate is also intensified. As a result, gas sealability between the protruded portion and the through hole in the substrate is improved.
The molding apparatus for the conductive plate according to a second aspect of the invention includes molds, a filler for filling the molds with the raw powder, a heating device for heating the raw powder and punches for forming the raw powder with pressure. The substrate having the through holes provided at predetermined positions is prepared and the mold contains the housing portions each having an opening corresponding to the through hole in the substrate. The substrate is sandwiched such that the housing portion corresponds to the through hole in the substrate. The filler fills the housing portion with the raw powder through the through hole. The heating device heats the raw powder filled in the housing portion through the through hole. The punches are slidably disposed so as to form the raw powder filled in the housing portion through the through hole with pressure.
The molding apparatus according to the second aspect of the invention can form the respective protruded portions integrally with the substrate by heating the raw powder filled in each housing portion in both dies under pressure. For that reason, when the conductive plate of this type is formed, it is not necessary to prepare the protruded portions preliminarily, so that the work for molding the protruded portions independently can be abolished. Further, it is also possible to abolish the work for fitting the independently formed protruded portions in the through holes in the substrate. As a result, this type of the conductive plate can be formed efficiently in a short time and at a low cost.
In the molding method for the conductive plate according to a third aspect of the invention, a mold is filled with raw powder comprising a mixture of conductive powder with binder resin. Then, current is supplied to raw powder filled in the mold so as to heat the raw powder with heat generated by resistance of raw powder, and then, the raw power heated in said mold is pressureized so as to form said conductive plate.